System for generating electricity using a chemical heat engine and piezoelectric material

ABSTRACT

A system for generating electrical power supply signals includes at least one heat engine having a chamber that undergoes heating/cooling cycle and corresponding pressure variations. At least one piezoelectric transducer is deformed in response to the pressure variations of the heat engine. A power converter transforms the electric signals generated in response to deformation of the piezoelectric transducer(s) to a desired electrical power supply signal. The heat engine preferably uses a geothermal source of cold and an ambient source of hot or vice-versa. Hydrogen can be used as a working fluid, and metal hydride material can be used for absorbing and desorbing hydrogen during the cycle of heating and cooling of the heat engine. A phase change material can also be used. The power converter preferably includes an electromechanical battery with a flywheel storing rotational energy and possibly an electrostatic motor that adds rotational energy to the flywheel.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.11/530,147, filed Sep. 8, 2006, to be issued as U.S. Pat. No. 7,439,630,on Oct. 21, 2008, which is hereby incorporated by reference herein inits entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates broadly to mechanisms for generating electricity.More particularly, this invention relates to mechanisms for generatingelectricity using piezoelectric materials.

2. State of the Art

Piezoelectricity is the result of charge displacement within acrystalline structure which lacks a central symmetry. Piezoelectricelements when subjected to a mechanical load (e.g., vibration,compression, and/or flexing) induce an electrical charge on oppositefaces of a piezoelectric material. In prior art piezoelectric elementshave been used for actuators, transducers, resonators, transformers,micro generators, and sensors of all types. Recently piezoelectricelements have been researched and developed for energy scavenging. Thepiezoelectric element functions as a capacitor in response to stress orstrain.

When a piezoelectric material is subjected to a compressive or tensilestress, an electric field is generated across the material, creating avoltage gradient and a subsequent current flow due to compressive ortensile stress which seeks equilibrium. The current flow is provided bya conductive material that allows the unequal charge of thepiezoelectric material to equalize by moving the unequal charge off fromthe piezoelectric material. Piezoelectric materials generate highvoltage and low current electricity. The piezoelectric effect isreversible in that piezoelectric material, when subjected to anexternally applied voltage, can change shape. Direct piezoelectricity ofsome substances (e.g., quartz, Rochelle salt) can generate voltagepotentials of thousands of volts.

Piezoelectric materials store energy in two forms, as an electricalfield, and as a mechanical displacement (strain). The relationshipbetween strain and the electric field is given by SC=1/ST (SR−(d*e))where “SC” is the compliance of the piezoelectric element in a constantelectric field, “SR” is the mechanical deformation and “d” is thepiezoelectric charge constant. The charge produced when a pressure isapplied is: Q=d*P*A, where P is the pressure applied and A is the areaon which the pressure is applied. Utilizing multiple piezoelectricstacks on top of one another and connecting them in parallel increasesthe charge in relationship to pressure. The output voltage generated canbe expressed as the total charge of the stack divided by the capacitanceof the stack.

In the prior art, piezoelectric materials have been used to scavengeenergy from vibration energy induced by wind, ocean waves, ambientsound, automobile traffic, the deformation of an automobile tire, andthe foot strike of a human being on a floor. However, the prior artmethodologies have resulted in very low power output, which makes suchsolutions suitable only for low power applications.

Thus, there remains a need in the art for systems and methodologies thatgenerate electricity by applying pressure gradients to piezoelectricmaterial in manner that is suitable for a wide range of power supplyapplications, such as residential or commercial power supplyapplications.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide systems andcorresponding methodologies that apply cyclic pressure gradients topiezoelectric material to generate corresponding electrical signals thatcan be used to generate electrical power suitable for a wide range ofpower supply applications, such as residential or commercial powersupply applications.

It is another object of the invention to provide such systems andmethodologies that utilize a chemical heat engine to apply the pressuregradients to the piezoelectric material.

It is another object of the invention to provide such systems andmethodologies that utilize environmentally friendly, low-cost geothermaland ambient sources of hot and cold to power the chemical heat engine.

It is a further object of the invention to provide power generationsystems and methodologies that convert electrical energy output by apiezoelectric source to mechanical energy stored by a rotating flywheelof an electro-mechanical battery, and that converts the mechanicalenergy stored by the flywheel to electrical energy for output therefrom.

It is also an object of the invention to provide efficient conversion ofthe electrical energy output by a piezoelectric source to mechanicalenergy stored by the rotating flywheel of the electro-mechanicalbattery.

In accord with these objects, which will be discussed in detail below, asystem (and corresponding methodology) for generating electrical signalsincludes at least one heat engine having a chamber that undergoes acycle of heating and cooling and corresponding pressure variations. Atleast one piezoelectric transducer, which is operably coupled to theheat engine, is deformed in response to the pressure variations of theheat engine. A power converter can be used to transform the electricsignals generated in response to deformation of the at least onepiezoelectric transducer to a desired electrical power supply signal.The heat engine preferably uses a geothermal source of cold and anambient source of hot (typically used in the summer months), orvice-versa (typically used in the winter months).

It will be appreciated that the heat engine can readily be adapted toundergo large, high frequency pressure variations and thus producelarge, high frequency stresses and corresponding large cyclicaldeformations of the piezoelectric transducer. Such deformations causehigh voltage, low current pulses that are transformed by the powerconverter.

In the preferred embodiment, the power converter includes anelectromechanical battery with a flywheel storing rotational energy andan electrostatic motor that adds rotational energy to the flywheel. AMarx generator can be used to generate a sequence of stepped-up voltagepulses to increase the repulsive forces that drive the electrostaticmotor. The electromechanical battery can readily be adapted to providepower supply signals that are suitable for a wide variety ofapplications, such as residential or commercial power supplyapplications.

In the preferred embodiment, the heat engine uses hydrogen as a workingfluid within its chamber as well as metal hydride material for absorbingand desorbing hydrogen during the cycle of heating and cooling of theheat engine. A phase change material can also be used. In anotheraspect, an apparatus for energy conversion includes an electromechanicalbattery and an electrostatic motor. The electromechanical batteryincludes a flywheel storing rotational energy. The electrostatic motoradds rotational energy to the flywheel.

Additional objects and advantages of the invention will become apparentto those skilled in the art upon reference to the detailed descriptiontaken in conjunction with the provided figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a block diagram of a piezoelectric power generator system inaccordance the present invention working in one mode of operation.

FIG. 1B is a block diagram of a piezoelectric power generator system inaccordance the present invention working in a second mode of operation.

FIG. 1C is an exemplary Pressure-Temperature curve that illustrates theheating/cooling/pressure cycle of the heat engine of FIGS. 1A and 1B.

FIG. 2 is a functional block diagram of an exemplary power conversionapparatus for use in the system of FIGS. 1A and 1B.

FIG. 3 is a schematic diagram of the power conversion apparatus of FIG.2.

FIG. 4 is a cross-section schematic illustrating components of theelectrostatic motor of FIG. 3.

FIG. 5 is a schematic diagram of the interface circuitry of FIG. 3

FIG. 6 is a schematic diagram of the Marx generator circuit of FIG. 5.

FIG. 7 is a block diagram of an alternate embodiment piezoelectric powergenerator system in accordance the present invention working in one modeof operation.

FIG. 8 is a block diagram of a controller that carries out automaticpressure adjustments to the chambers of the heat engines of FIG. 7.

FIGS. 9A and 9B are schematic diagrams of tube-in-tube designs for thefluid supply paths that fluidly couple the heat engines of FIG. 7.

FIG. 10 is a schematic diagram of a tube-in-tune design for the heatengine(s) of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Turning now to FIG. 1, there is shown a pictorial illustration of apiezoelectric energy generator system 10 in accordance with the presentinvention. The system 10 includes a geothermal exchange heat engine 12that includes a housing 14 with a thermal insulating liner (not shown),which can be realized with a space filled with an aerogel or othersuitable thermal insulating material. One end of the housing 14 supportsa cold-side heat exchanger 16 (e.g., plate-type or tube-type heatexchanger) that is realized from a thermally conductive material such ascopper, cooper alloys, stainless steel, or pyrolytic graphite. The otherend of the housing 14 supports a hot-side heat exchanger 18 (e.g.,plate-type or tube-type heat exchanger) that is also realized from athermally conductive material such as copper, cooper alloys, stainlesssteel, or pyrolytic graphite. A sealed chamber 20 is disposed betweenthe cold-side heat exchanger 16 and the hot-side heat exchanger 18. Thechamber 20 is in thermal contact with both the cold-side heat exchanger16 and the hot-side heat exchanger 18. The chamber 20 is filled withhydrogen working fluid 22. The chamber 20 also contains at least onemetal hydride material 24 capable of hydrogen absorption and desorptionand preferably at least one phase change material 26 in thermal contactwith the hydrogen working fluid.

The at least one metal hydride material 24 is held in one or more bedsor other storage container(s). The at least one metal hydride materialmay comprise:

-   -   i) lithium nitride;    -   ii) magnesium hydride;    -   iii) lanthium nickel hydride (LaNi5H6), or modifications of        lanthium nickel hydride by some substitution of either the La or        Ni;    -   iv) vanadium-based solid solution which have the general formula        (V1−xTix)1−y My, where M is usually a Group VI to VIII metal        such as Fe, Ni, Cr, or Mn; and/or    -   v) Laves phase hydrides which have the general formula, AB2,        where A is usually a rare earth, Group III or Group IV metal and        B is usually a Group VIII metal, but may also be a metal from        Groups V, VI or VII.

The at least one phase change material 26 is held in a storage containerand may comprise zeolite, eutectic alloys, paraffins, organic compounds,salt hydrates, carbonates, nitrates, polyhydric alcohols and metals.

The heat engine 12 also includes one or more piezoelectric transducerelements 28 of piezoelectric material. The piezoelectric material can bequartz, Rochelle salt, barium titanate, zinc oxide, lead titanate, leadzirconate titanate, lead lanthanum zirconate titanate, lead magnesiumniobate, potassium niobate, potassium sodium niobate, potassiumtantalate niobate, lead niobate, lithium niobate, lithium tantalate,fluoride poly(vinylidene flouride or other suitable material. Thepiezoelectric transducer element(s) 28 can be disposed adjacent thechamber 20 in contact with the chamber wall or liner and in indirectcontact with the hydrogen working fluid 22 such that pressure changes ofthe hydrogen working fluid 22 are applied to the piezoelectrictransducer element(s) 28 to impart mechanical stress therein.Alternatively, the piezoelectric transducer element(s) 28 can bedisposed within the chamber 20 (running lengthwise or width-wise, orboth) in direct contact with the hydrogen working fluid 22 such thatpressure changes of the hydrogen working fluid 22 are applied to thepiezoelectric transducer element(s) 28 to impart mechanical stresstherein. The piezoelectric transducer element(s) 28 can be configured asa diaphragm membrane, beam, plate, rod and/or fiber.

At least one pair of electrodes 30A, 30B are electrically coupled to thepiezoelectric transducer element(s) 28. The electrodes 30A, 30B outputelectrical signals generated by the piezoelectric transducer element(s)as a result of the mechanical stress induced therein by pressure changesof the hydrogen working fluid 22.

A supply of cold fluid is supplied to the cold-side heat exchanger 16,and a supply of hot fluid is supplied to the hot-side heat exchanger 18.The supply of cold fluid preferably includes a circulator (e.g., pump,fan) for providing a continuous supply of cold fluid to the cold-sideheat exchanger 16 over multiple heating/cooling cycles of the heat pumpengine 12. The supply of hot fluid preferably includes a circulator(e.g., pump, fan) for providing a continuous supply of hot fluid to thehot-side heat exchanger 18 over multiple heating/cooling cycles of theheat engine 12. In one mode of operation shown in FIG. 1A, when theambient air is warmer than the deep ground temperature, the supply ofcold fluid is produced by a geothermal source of cold 32 and the supplyof hot fluid is produced from ambient air 34. The geothermal source ofcold 32 can be ground water that is extracted from a well or a body ofwater (e.g., pond or lake). It can also be a fluid, such as water orair, which is cooled as it passes through a conduit in thermal contactwith the ground. In a second mode of operation shown in FIG. 1B, whenthe deep ground temperature is warmer than the ambient air, the supplyof cold fluid supplied to the cold-side heat exchanger 16 is producedfrom ambient air 32′, while the supply of hot fluid to the hot-side heatexchanger is produced by a geothermal source of “hot” 34′. Thegeothermal source of hot 34′ can be ground water that is extracted froma well or a body of water (e.g., pond or lake). It can also be a fluid,such as water or air, that is heated as it passes through a conduit inthermal contact with the ground. It will be appreciated that valves andpipes may be utilized to permit the system to switch between modesdepending upon the relative temperatures of the sources.

Where the geothermal source is a source of cold thermal energy,thermo-acoustic refrigeration can also be used to further the efficiencyof the system. In particular, an acoustic source capable of generating ashock wave may be placed in a subterranean well and operably coupled tothe hot-side and/or cold side heat exchangers of the engine. Acousticrefrigeration is a form of heat pump that uses sound waves to eitherincrease temperature or reduce temperature. Generally, a containerfilled with a working fluid is submerged within a subterranean well. Anacoustic transducer generates a shockwave, which compresses the gas infront of the shockwave while reducing the density of the gas behind theshockwave. As the gas is compressed by the shockwave, the temperature ofthe gas increases. As the gas is expanded behind the shockwave, thetemperature of the gas decreases. The heated compressed gas in front ofthe shockwave can be used as a source of hot for supply to the hot-sideheat exchanger 18 of the engine 12. The cool area behind the shockwavecan be used as a source of cold for supply to the cold-side heatexchanger 16 of the engine 12.

A fluid supply source 38 and a pressure control mechanism 40 can beprovided. The fluid supply source 38 and the pressure control mechanism40 cooperate to add working fluid 22 to the chamber 20 and adjust thepressure of the working fluid 22 in the chamber 20 as needed. Whenhydrogen is used as the working fluid, the fluid supply source 38 can berealized by a vessel of hydrogen or possibly an apparatus for producinghydrogen by electrolysis of water. The pressure control mechanism 40 canbe realized by a pump and valve assembly, which can possibly include ableed valve for bleeding excess pressures to the ambient environment asneeded.

The heat engine 12 generally operates as follows. In a continuousmanner, the source of cold 32 continuously supplies cold fluid to thecold-side heat exchanger 16 and the source of hot 34 continuouslysupplies hot fluid to the hot-side heat exchanger 18. The temperaturedifferential is utilized to generate work. More particularly, and asdescribed in more detail hereinafter with reference to FIG. 1C, thetemperature difference is used to cause the temperature of the hydrogenworking fluid, the metal hydride(s) and the phase change material(s) (ifany) in the chamber 20 to cycle in order to induce pressure changestherein. The pressure changes in the chamber 20 apply correspondingcompressive and decompressive forces on the piezoelectric transducerelement(s) 28, which induces mechanical stress therein. In response tosuch mechanical stress, the piezoelectric transducer element(s) 28 aredeformed in a cyclical manner. Such cyclical deformation causes thepiezoelectric material to generate a sequence of high voltage, lowcurrent electrical pulses (V+, V−) that are output by the electrode(s)30A, 30B electrically connected thereto.

FIG. 1C illustrates an exemplary compression-decompression cycle of theheat engine 12 of FIGS. 1A and 1B, although it should be appreciatedthat the cycle seen is merely schematic and not to scale. The cycleincludes 4 segments AB, BC, CD, DA. For purposes of explanation, it isassumed that the engine 12 starts at a temperature and pressure nearpoint A, which is preferably accomplished by controlling adjusting thepressure of the working fluid 22 within the vessel by operation of thepressure control mechanism 40. It is also assumed that the engine 12 hasa characteristic temperature T_(INT) whereby:

-   -   i) for temperature T_(INT), heat flowing into the chamber 20        from the hot-side heat exchanger 18 is substantially equal to        the heat flowing out of the chamber 20 to the cold-side heat        exchanger 16, which causes the temperature gradient within the        chamber 20 to remain substantially constant;    -   ii) for temperatures below T_(INT), heat flowing into the        chamber 20 from the hot-side heat exchanger 18 exceeds heat        flowing out of the chamber 20 to the cold-side heat exchanger        16, which causes the temperature gradient within the chamber 20        to increase; and    -   iii) for temperatures above T_(INT), heat flowing out of the        chamber 20 from the cold-side heat exchanger 16 exceeds the heat        flowing into the chamber 20 from the cold-side heat exchanger        18, which causes the temperature gradient within the chamber 20        to decrease.        The characteristic temperature T_(INT) is dictated by the        temperature of the hot-side heat exchanger and cold-side heat        exchanger (T_(HOT) and T_(COLD)), the relative thermal        conductivity of the hot-side and cold-side heat exchangers, the        relative size of the hot-side and cold-side heat exchangers.        Segment AB—Compression of Piezoelectric Transducer Element(s)

During segment AB, heat flowing into the chamber 20 from the hot-sideheat exchanger 18 dominates heat flowing out of the chamber 20 to thecold-side heat exchanger 16, which causes the temperature gradientwithin the chamber 20 to increase. Such heat increases the temperatureof the hydrogen working fluid 22, which causes a corresponding increaseof the pressure within the chamber 20 as shown. The volume of thehydrogen working fluid 22 remains substantially constant. The heat flowinto the chamber 20 will cause the temperature and pressure within thesealed chamber to reach point B, which is the criticalpressure/temperature point for absorption of hydrogen by the metalhydride material(s) 24. Some time at or before this point, if a phasechange material is present in the chamber, the material will absorb heatand change phase, thereby storing thermal energy. In any event, at thecritical pressure/temperature point for the absorption of hydrogen bythe metal hydride, segment BC begins.

Segment BC—Hydrogen Absorption by Metal Hydride(s)

During segment BC, the metal hydride material(s) 24 absorb the hydrogenworking fluid 22. This absorption is an exothermic reaction, whichreleases heat and maintains the pressure of the hydrogen working fluid22 substantially constant at the critical pressure. During theabsorption reaction, the pressure within the chamber 20 is maintained ata relatively constant pressure, which corresponds to the criticalpressure of the metal hydride material(s) 24. The absorption reactioncontinues until the metal hydride material(s) 24 is(are) saturated. Uponsaturation, the heat that was released earlier during the exothermicreaction can cause a spike or increase in the temperature of the chamber20 and thus cause a corresponding increase/spike in pressure to a PointC as shown. At this point, segment CD begins.

Segment CD—Decompression of Piezoelectric Element(s)

During segment CD, heat flowing out of the chamber 20 from the cold-sideheat exchanger 16 dominates the heat flowing into the chamber 20 fromthe cold-side heat exchanger 18, which causes the temperature gradientwithin the chamber 20 to decrease. This causes the temperature of thehydrogen working fluid 22 and a corresponding decrease of the pressurewithin the chamber 20 to decrease as shown. When the temperature andpressure of the chamber 20 drop below a critical temperature andpressure for hydrogen desorption (point D), segment DA begins.

Segment DA—Hydrogen Desorption by Hydride

When the temperature and pressure within the chamber 20 drop below thecritical temperature and pressure point D, the metal hydride material(s)desorbs hydrogen by an endothermic reaction that absorbs heat, therebyaccelerating the decrease in temperature of the chamber 20 and thecooling mode cycle time. In addition, where phase change material ispresent, the phase change material releases its thermal energy andreverts to its original phase. The segment DA continues until point Awhere the hot-side heat exchanger 18 can support an increase in thetemperature of the hydrogen working fluid 22. At that point the cyclerestarts.

The pressure level increases from P_(MIN) to P_(MAX) during the cycle asshown to apply corresponding compressive forces and stress on thepiezoelectric transducer element(s) 28. The pressure level decreasesfrom P_(MAX) to P_(MIN) during the cycle as shown to apply correspondingdecompressive forces and stress on the piezoelectric transducerelement(s) 28. The alternating compressive/decompressive forces andstress applied to the piezoelectric transducer element(s) 28 duringsuccessive heating and cooling cycles of the heat engine 12 causesdeformation of the piezoelectric transducer element(s) 28 in a cyclicalmanner. Such cyclical deformation of the piezoelectric materialgenerates a sequence of high voltage, low current electrical pulses thatare output by the electrode(s) 30A, 30B electrically connected thereto.

As previously mentioned, one or more phase change materials 26 may beused as part of the heat engine 12 as described above. The phase changematerial(s) 26 are disposed in thermal contact with the hydrogen workingfluid 22. The phase change material(s) 26 is(are) tuned to absorb heatat or near the temperature of Point B for absorption of hydrogen workingfluid 22 by the metal hydride material(s) 24, and release heat duringthe desorption of hydrogen working fluid 22 by the metal hydridematerial(s) 24 during segment DA. This aids in reducing the cycle timeof the heat engine 12 and the power generated by the heat engine 12.

The preferred embodiment of the system 10 includes a power converter 36that converts the electrical signals output by the piezoelectrictransducer element(s) 28 over the electrode pair(s) 30A, 30B into adesired electrical output form. The electrical output produced by thepower converter 36 can be adapted for a wide range of power supplyapplications, such as residential or commercial power supplyapplications. It can be an AC power supply signal or a DC power supplysignal. In the preferred embodiment, the electrical output produced bythe power converter 36 is a standard AC power supply signal typicallysupplied by mains power (e.g., a 60 Hz 120V AC electrical supplysignal).

As depicted schematically in FIG. 2, the power converter 36 ispreferably realized by an assembly that includes an electrostatic motor51 and an electro-mechanical battery 53. As best shown in FIG. 3, theelectro-mechanical battery 53 includes a cylindrical rotor 61 with anarray of permanent magnets that provide a uniform dipole field (i.e.,Halbach array). A high-speed flywheel is integral to the rotor 61. Therotor and flywheel are suspended on magnetic bearings (or other suitablelow friction supports) and spin in vacuo, inside a hermetically sealedchamber. The high speed flywheel is used for energy storage andextraction. Stator windings 63A, 63B are disposed within the interiorspace of the cylindrical rotor 61. The stator windings 63A, 63B areinductively coupled to the magnetic field provided by the rotating arrayof magnets of the rotor 61. Power electronics 55 interface to statorwindings 63A, 63B to extract energy from the rotating flywheel andconvert such energy into the desired electrical power supply signal thatis output therefrom. The electro-mechanical battery 53 is similar tothat described in U.S. Pat. Nos. 5,705,902 and 6,396,186, hereinincorporated by reference in their entirety.

Rotational energy is added to the flywheel of the electro-mechanicalbattery 53 by operation of an electrostatic motor 51. Turning to FIG. 3in conjunction with FIG. 4, the electrostatic motor 51 includes acylindrical rotor 71 configured to have multiple conductive regions 72evenly spaced about its interior surface and electrically insulated fromone another. The rotor 71 of the electrostatic motor 51 is suspended onmagnetic bearings (or other suitable low-friction supports) and iscoupled to the rotor 61 of the electro-mechanical battery 53 such thatrotation of the rotor 71 causes rotation of the rotor 61 of theelectro-mechanical battery 53. A stator assembly 73 is disposed withinthe interior space of the cylindrical rotor 71.

As shown in FIG. 4, the stator assembly 73 supports a plurality ofelectrodes 74 that are evenly spaced apart from one another such thatthey lie in close proximity to the conductive regions 72 of the rotor71. Contact brushes 76 extend from the stator assembly 73 (or possiblyfrom the stator electrodes themselves 74). The contact brushes 76 areelectrically connected to corresponding stator electrodes 74 and extendradially outward to contact the conductive regions 72 of the rotor 71. Aconductor 78 extends along the arms of the stator from the electrodes tothe base. The conductors 78 and electrodes 74 of the stator assembly 73are logically partitioned into two groups (e.g., positive and negativepolarities). The positive and negative polarity electrodes 74 aredisposed one after the other in alternating fashion about the peripheryof the stator assembly 73. The positive polarity electrodes of thestator assembly 73 are charged with a positive voltage potential, whilethe negative polarity electrodes of the stator assembly 73 are chargedwith a negative voltage potential. This configuration allows repulsiveCoulomb forces between the electrodes 74 of the stator assembly 73 andthe conductive regions 72 of the rotor 71 to induce rotation of therotor 71.

In an alternate embodiment, the contact brushes 76 can be omitted andcorona discharge across the medium between the stator electrodes 74 andthe conductive regions 72 of the rotor 71 can be used to deposit chargeon the conductive regions 72 of the rotor 71. This configuration alsoresults in alternately charged regions of the rotor, which repel theneighboring like-charged stator electrodes.

Referring now to FIGS. 2 and 3, interface circuitry 57 is providedbetween the electrode pair(s) 30A, 30B of the piezoelectric transducerelement(s) 28 and the conductors 78 of the stator assembly 73. Theinterface circuitry 57 transfers the electrical energy output from thepiezoelectric transducer element(s) 28 to the conductors 78 andelectrodes 74 of the stator assembly 73 in order to induce rotation ofthe rotor 71.

As shown in FIG. 5, the interface circuitry 57 preferably includes anAC/DC rectifier, a filter capacitor, and a Marx generator circuit asshown. The AC/DC rectifier converts the AC signal output from thepiezoelectric transducer element(s) 28 into DC current, the filtercapacitor smoothes the resultant signal to generate a DC chargingsignal, and the Mark generator circuit converts the DC charging signalto a high voltage pulse.

The Marx generator circuit, which was first described by Erwin Marx in1924, generates a high voltage pulse. As shown in FIG. 6, a number ofcapacitors are charged in parallel to a given voltage, V, and thenconnected in series by spark gap switches, ideally producing a voltageof V multiplied by the number, n, of capacitors (or stages). Due tovarious practical constraints, the output voltage is usually somewhatless than n*V. In the ideal case, the closing of the switch closest tothe charging power supply applies a voltage 2*V to the second switch.This switch will then close, applying a voltage 3*V to the third switch.This switch will then close, resulting in a cascade down the generator(referred to as erection) that produces n*V at the generator output(again, only in the ideal case). The first switch may be allowed tospontaneously break down (sometimes called a self break) during chargingif the absolute timing of the output pulse is unimportant. However, itis usually intentionally triggered by mechanical means (reducing the gapdistance), triggered electrically, triggered via a pulsed laser, or byreducing the air pressure within the gap after all the capacitors havereached full charge. The charging resistors, Rc, are sized for bothcharging and discharging. The charging resistors can be replaced withinductors for improved efficiency and faster charging.

In an alternate embodiment, the electrostatic motor 51 and itssupporting circuitry can be substituted by components that transform theelectrical energy provided by the output of the piezoelectric transducerelement(s) 28 to electromagnetic forces that induce rotational energy ofthe rotor 61 of the electromechanical battery 53 and thus add rotationalenergy to the flywheel of the electromechanical battery. For example,the high voltage, low current electrical signals generated by thepiezoelectric transducer element(s) 28 can be supplied to an interfacecircuit that cooperates with additional stator windings of theelectro-mechanical battery (or possibly to the same stator windings usedfor energy extraction in a phased design) to generate a magnetic fieldthat is inductive coupled to the magnetic field provided by the rotatingarray of magnets of the rotor 61 of the electro-mechanical battery 53 inorder to induce rotation of its rotor 61 and add rotational energy toits flywheel.

FIG. 7 illustrates an alternate embodiment of the present invention,which includes two heat engines 12 ₁ and 12 ₂ whose chambers are fluidlycoupled together by two fluid lines. One of the fluid lines carriesworking fluid from the chamber of heat engine 12 ₁ to the chamber ofheat engine 12 ₂, while the other fluid line carries working fluid fromthe chamber of heat engine 12 ₂ to the chamber of heat engine 12 ₁. Flowcontrol valves 42A₁, 42A₂, 42B₁, 42B₂ are disposed at the input andoutput of the two fluid lines for the respective chambers. A fluidsupply source 38′ and a pressure control mechanism 40′ are fluidlycoupled to one of the two fluid lines between the respective input andoutput valves as shown. The fluid supply source 38′ and the pressurecontrol mechanism 40′ cooperate to add working fluid 22 to the chambersof the two engines and adjust the pressure of the working fluid in thechambers of the two engines as needed. When hydrogen is used as theworking fluid, the fluid supply source 38′ can be realized by a vesselof hydrogen or possibly an apparatus for producing hydrogen byelectrolysis of water. The pressure control mechanism 40′ can berealized by a pump and valve assembly, which can possibly include ableed valve for bleeding excess pressures to the ambient environment asneeded. The input and output valves can be open and closed as needed toadjust the amount/pressure of working fluid in each one of the chambers.For example, in the configuration shown, the pressure of the chamber forthe engine 12 ₁ can be adjusted by opening the output valve 42B₁ andclosing the other valves 42B₂, 42A₁, 42A₂. Similarly, the pressure ofthe chamber for the engine 12 ₂ can be adjusted by opening the outputvalve 42B₂ and closing the other valves 42B₁, 42A₁, 42A₂.

During normal operation, the valves 42A₁, 42A₂, 42A₁, 42A₂ are openedand the two heat engines 12 ₁, 12 ₂ are operated such that their heatingand cooling cycles are out of phase with one another. Consider forexample that the heat engines 12 ₁ and 12 ₂ are both configured to carryout the heating and cooling cycle of FIG. 1C. In this configuration, theinitial pressure of the heat engine 12 ₁ can be initialized to beginoperation at or near point C, while the initial pressure of the heatengine 12 ₂ can be initialized to begin operation at or near point A.The heat engines 12 ₁ and 12 ₂ cycle through their heating and coolingcycles as follows:

Heat Engine 12₁ Heat Engine 12₂ Segment CD Segment AB Segment DA SegmentBC Segment AB Segment CD Segment BC Segment DAThis configuration is advantageous because it reduces the heating andcooling cycle time and thus increases the frequency of the pressurevariations produced by the chemical heat engines.

FIG. 8 shows a schematic illustration of a pressure controller. Thepressure controller can be used to automatically adjust and maintain theworking fluid pressures within the chambers of the heat engines in theirdesired operating range. Such control may be necessary if hydrogen leaksfrom the system and/or to accommodate changing temperatures for thesupply of hot and/or cold (e.g., changing ambient air temperatures). Thecontroller is preferably interfaced to temperature sensors that measurethe temperature of the hot and cold supply as well as to theactuation/control function of the valves 42A1, 43A2, 42B1, 43B2, thefluid supply source 38′ and the pressure control mechanism 40′. Thecontroller implements a control algorithm (preferably using a look-uptable or the like) that calculates the appropriate chamber pressurelevel(s) based on the temperature of the hot and cold supply as outputby the temperature sensors. The controller then automatically cooperateswith the actuation/control function of the valves 42A1, 43A2, 42B1,43B2, the fluid supply source 38′ and the pressure control mechanism 40′as needed to adjust pressure of the chambers to the desired pressurelevel. A similar control scheme can be used to automatically adjust thepressure within the single engine configuration of FIGS. 1A and 1B.

FIG. 9A illustrates an embodiment for the system of FIG. 7 wherein thefluid supply lines that fluidly couple the two engines are realized by atube-in-tube design. The outer tube supports the one or morepiezoelectric transducer elements 28′ of the respective engine. Theinner tube is a flexible gas pressure tube that is fluidly coupledbetween the chambers of the engine and thus become extensions of suchchambers. During the heating/cooling/pressure cycles of the two engines,the oscillating pressure variations generated by the two engines willflow through the flexible gas pressure tubes, which appliescorresponding compressive/decompressive forces to the one or morepiezoelectric transducer elements 28′ as described herein. In thisconfiguration, the piezoelectric transducer element(s) 28′ of therespective engine can be remotely located with respect to the vesselcontaining the hydride material and PCM material of the engine.

FIG. 9B illustrates another embodiment for the system of FIG. 7 whereinthe fluid supply lines that fluidly couple the two engines are realizedby a novel tube-in-tube design. An outer tube supports two inner tubeswith one or more piezoelectric transducer elements therebetween. The twoinner tubes are fluidly coupled between the chambers of the two enginesand thus become extensions of such chambers. During theheating/cooling/pressure cycles of the two engines, the oscillatingpressure variations generated by the two engines will flow through theflexible gas pressure tubes. Such pressure variations are preferably outof phase with one another and thus provide an oscillating pressuredifferential therebetween. This oscillating pressure differential isused to apply compressive/decompressive forces that deform thepiezoelectric transducer element(s) disposed between the two flexiblegas pressure tubes (for example, by oscillating deformation of apiezoelectric diaphragm). In this configuration, the piezoelectrictransducer element(s) of the respective engine can be remotely locatedwith respect to the vessel containing the hydride material and PCMmaterial of the engine.

As shown in FIG. 10, the heat engines described herein can be arrangedin a tube-in-tube type configuration. In this configuration, an innertube 81 carries the source of hot (or cold). The exterior of the outertube 83 is subjected to the source of cold (or hot). The inner tube 81and outer tube 83 are realized from thermally conductive material asdescribed herein and thus function a heat exchangers. The hydrogenworking fluid, metal hydride material and possibly phase change materialof the engine are disposed in a closed space between the inner tube 81and outer tube 83. The piezoelectric pressure transducer(s) of theengine can also be located within the closed space between the innertube 81 and outer tube 83, or can possibly be located with a fluid paththat is fluidly coupled to this closed space, for example, in a fluidsupply line similar to that shown in FIGS. 9A and 9B.

There have been described and illustrated herein several embodiments ofa system and methodology for generating electricity using piezoelectricmaterial(s). While particular embodiments of the invention have beendescribed, it is not intended that the invention be limited thereto, asit is intended that the invention be as broad in scope as the art willallow and that the specification be read likewise. Thus, whileparticular heat engine configurations have been disclosed, it will beappreciated that other heat engine configurations can be used as well.Also, while particular sources of hot and cold have been described, itis contemplated that the heat engine can be powered by other sources ofhot and cold. For example, seawater and ambient air can be used assources of cold and hot or vice versa, depending on the season. Inaddition, while particular types of electrostatic motors andelectro-mechanical batteries have been disclosed, it will be understoodthat other types can be used. For example, it is contemplated that thepermanent array of magnets of the electromechanical battery can be partof the stator and the windings that are electromagnetically coupledthereto can be part of the rotor. In another example, the statorassembly of the electrostatic motor can be disposed outside the rotor ofthe electrostatic motor. Also, while preferred electronic circuitry andcomponents have been described, it will be recognized that otherelectronic circuitry and components can be similarly used. Moreover,while particular materials and designs have been disclosed in referenceto the heat engine and piezoelectric transducer elements, it will beappreciated that other configurations could be used as well. It willtherefore be appreciated by those skilled in the art that yet othermodifications could be made to the provided invention without deviatingfrom its spirit and scope as claimed.

1. A system for generating electrical signals comprising: at least oneheat engine having a subterranean geothermal energy source, the heatengine adapted to undergo a cycle of heating and cooling and to generatecorresponding pressure variations within a chamber; at least onepiezoelectric transducer operably disposed within the chamber thatdeforms in response to the pressure variations within the chamber andgenerates an electrical output signal as a result of the deformation. 2.A system according to claim 1 further comprising: a power converteroperably coupled to the at least one piezoelectric transducer thattransforms said electrical output signals to a desired electrical powersupply signal.
 3. A system according to claim 1, wherein: thesubterranean geothermal energy source is a subterranean geothermalsource of cold used in conjunction with an ambient source of hot.
 4. Asystem according to claim 1, wherein: the subterranean geothermal energysource is a subterranean geothermal source of hot used in conjunctionwith an ambient source of cold.
 5. A system according to claim 1,wherein: hydrogen is disposed as a working fluid within the heat engine.6. A system according to claim 5, wherein: at least one metal hydridematerial is disposed within the heat engine, the metal hydride materialfor absorbing and desorbing hydrogen during the cycle of heating andcooling of the heat engine.
 7. A system according to claim 6, wherein:at least one phase change material is disposed within the heat engine.8. A system according to claim 7, wherein: the metal hydride materialabsorbs hydrogen at a first pressure and a first temperature, the firsttemperature corresponding to a temperature at which the phase changematerial releases heat.
 9. A system according to claim 8, wherein: themetal hydride material desorbs hydrogen at a second pressure and asecond temperature, the second temperature corresponding to atemperature at which the phase change material absorbs heat.
 10. Asystem according to claim 2, wherein: the power converter comprises anelectromechanical battery with a flywheel for storing rotational energy.11. A system according to claim 10, wherein: the power converterincludes means for transforming rotational energy from the flywheel intothe desired electrical power supply signal.
 12. A system according toclaim 10, wherein: the electromechanical battery includes a rotor thatis electromagnetically coupled to a stator, the rotor being operablycoupled to the flywheel, and one of the rotor and stator comprises apermanent array of magnets.
 13. A system according to claim 10, wherein:the power converter includes an electrostatic motor operably coupled tothe electromechanical battery for adding rotational energy to theflywheel.
 14. A system according to claim 13, wherein: the electrostaticmotor includes a rotor and stator that are rotated relative to oneanother via repulsive coulomb forces, said rotor operably coupled to theflywheel of the electromechanical battery.
 15. A system according toclaim 13, wherein: the power converter comprises interface circuitryoperably coupled between the at least one piezoelectric transducerelement and the electrostatic motor.
 16. A system according to claim 15,wherein: the interface circuitry comprises a Marx generator circuit. 17.A system according to claim 16, wherein: the interface circuitrycomprises an AC-DC rectifier and a filter capacitor that cooperate togenerate a charging voltage signal for input to the Marx generatorcircuit.